Genetic diversity and population structure of the tsetse fly Glossina fuscipes fuscipes (Diptera: Glossinidae) in Northern Uganda: Implications for vector control

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Date
2017Author
Opiro, Robert
Saarman, Norah P.
Echodu, Richard
Opiyo, Elizabeth A.
Dion, Kirstin
Halyard, Alexis
Dunn, Augustine W.
Aksoy, Serap
Caccone, Adalgisa
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Uganda is the only country where the chronic and acute forms of human African Trypanosomiasis
(HAT) or sleeping sickness both occur and are separated by < 100 km in areas north
of Lake Kyoga. In Uganda, Glossina fuscipes fuscipes is the main vector of the Trypanosoma
parasites responsible for these diseases as well for the animal African Trypanosomiasis
(AAT), or Nagana. We used highly polymorphic microsatellite loci and a mitochondrial
DNA (mtDNA) marker to provide fine scale spatial resolution of genetic structure of G. f. fuscipes
from 42 sampling sites from the northern region of Uganda where a merger of the two
disease belts is feared. Based on microsatellite analyses, we found that G. f. fuscipes in
northern Uganda are structured into three distinct genetic clusters with varying degrees
of interconnectivity among them. Based on genetic assignment and spatial location, we
grouped the sampling sites into four genetic units corresponding to northwestern Uganda in
the Albert Nile drainage, northeastern Uganda in the Lake Kyoga drainage, western Uganda
in the Victoria Nile drainage, and a transition zone between the two northern genetic clusters
characterized by high level of genetic admixture. An analysis using HYBRIDLAB supported
a hybrid swarm model as most consistent with tsetse genotypes in these admixed samples.
Results of mtDNA analyses revealed the presence of 30 haplotypes representing three
main haplogroups, whose location broadly overlaps with the microsatellite defined clusters.
Migration analyses based on microsatellites point to moderate migration among the northern
units located in the Albert Nile, Achwa River, Okole River, and Lake Kyoga drainages,
but not between the northern units and the Victoria Nile drainage in the west. Effective
population size estimates were variable with low to moderate sizes in most populations and
with evidence of recent population bottlenecks, especially in the northeast unit of the Lake
Kyoga drainage. Our microsatellite and mtDNA based analyses indicate that G. f. fuscipes
movement along the Achwa and Okole rivers may facilitate northwest expansion of the Rhodesiense disease belt in Uganda. We identified tsetse migration corridors and recommend
a rolling carpet approach from south of Lake Kyoga northward to minimize disease
dispersal and prevent vector re-colonization. Additionally, our findings highlight the need for
continuing tsetse monitoring efforts during and after control.